A well known type of cracking catalyst is one formed by spray drying a mixture of an exchanged zeolite of the faujasite type, e.g. Y type of suitable low sodium content with peptized pseudoboehmite and clay. These are usually marketed as microspheres of about 50 to 70 micron average diameter. One problem associated with such catalysts is the nature of the abrasion resistance of the microspheres.
In order to improve the resistance to abrasion (for example as measured by its Abrasion Index by the test procedures described in Secor, et al, U.S. Pat. No. 4,010,116) of the above mixtures, various expedients have been proposed. These include the addition of crystalline silicate known as SMM (see Secor, et al, supra), ammonium polysilicates (see Lim, et al, U.S. Pat. No. 4,086,187), sodium silicate in limited quantities (see Lim, et al, Ser. No. 896,318; filed Apr. 14, 1978) and the in situ encapsulation of the zeolite silica with a silica-alumina gel (see Alfandi, et al, U.S. Pat. No. 4,412,995).
It has been shown that the thermal stability and the attrition resistance of catalysts composed of a zeolite and a matrix including clay is improved by the addition of alumina specifically if it be a suitably peptized pseudoboehmite added to the matrix prior to spray drying. Reference may be had to the copending application, Ser. No. 3,407, now U.S. Pat. No. 4,206,085 which one of us is a joint applicant.
Various patents relating to the use of silica-alumina sols and gels and sodium silicate in zeolite compositions for various purposes have been issued. Reference may be had to the following U.S. patents: Gladrow, No. 3,609,103, No. 3,449,265; Robbins, No. 3,558,476; Kiovsky, No. 3,641,090; Conde, No. 3,624,003; Hoffman, No. 3,972,835; Drost, No. 3,446,645; Scott, No. 3,451,948.
One of the inherent properties of catalysts of the aforesaid type is the tendency of the catalyst to promote the conversion of the petroleum fraction charged to the cracking process into coke. The coke deposits on the catalyst and deactivates the catalyst. Such catalysts also promote the production of gases such as hydrogen. Together these properties of the catalyst result in a decrease in the yield of hydrocarbons in the gasoline range.
While some coke is desirable to be deposited on the catalyst in order that it may permit the generation of a sufficiently high temperature in the regenerators, to produce the necessary reactivation of the catalyst by burning off the carbon, the excessive carbon deposit does introduce a problem in the regenerator as is well known in the prior art.
The hydrogen formation by a catalyst is associated with the dehydrogenation process and influences the production of unsaturated light hydrocarbons.
The cracking activity of a catalyst is determined on a laboratory bench scale by microactivity tests. As used in the following Examples 1-4, it is of the type reported in the Oil and Gas Journal issues of 1966, Volume 64, Number 39, Pages 84, 85, modified as reported in the issue of Nov. 22, 1971, Pages 60 through 63. In the following examples, the conditions were as follows:
The calcined catalyst formed into a pellet was first steamed at temperatures and times specified below and then used in cracking of a petroleum fraction under the following conditions. Oil charge was a wide boiling range high sulfur feed stock (boiling range about 430.degree. to 1000.degree. F.). The catalyst to oil ratio equaled 2.92. The weight hourly space velocity equaled 16.45 grams of oil per gram of catalyst per hour. The temperature of the reactor was 910.degree.. The percent conversion is reported as the volume of liquid condensate product of boiling point range of up to 421.degree. F. based on the volume of liquid charge. The percent conversion after the catalyst is calcined in air three hours at 1050.degree. F. and steamed for two hours at 1450.degree. F. and then subjected to the above test conditions, is termed M activity. When the calcined sample is steamed at 1500.degree. F. for two hours, it is termed the S activity. When the calcined sample is first steamed for two hours at 1550.degree. F., it is termed S+ activity.
The carbon producing property of a catalyst depends upon the activity of the catalyst measured by the percent conversion of the stock, for example as measured by said test. The greater the percent conversion, the greater is the percent of the feed stock that appears as carbon. The hydrogen production property of a catalyst is substantially independent of the percent conversion up to a limited upper value of M activity of about 75% as measured by the percent conversion in the above tests and at higher values of conversion increases rapidly with the percent conversion.
As a measure of the carbon conversion properties of a fresh catalyst, and to permit comparison between catalysts of different activity, the carbon conversion tendency is measured by its carbon production factor (CPF).
The carbon production factor is obtained by measuring the volume percent conversion in the above test (Cv) and the weight percent of carbon (Cw) deposited on the catalyst in the above test, based on the weight of the charge. For every conversion by the above test, which is more than 8% and less than 75.5% volume percent of the charge, the carbon production factor (CPF) is evaluated by the following equation (I): EQU CPF=Cw/e.sup.k Equation I
wherein:
k=(Cv-36)/36 PA1 k=(Cv-69)/5.9 PA1 k=0.0011 Cv-0.0476
At values of conversion equal to or greater than 75.5%, and equal to or less than 82%, volume percent conversion, the carbon production factor (CPF) is evaluated by the following equation (II): EQU CPF=Cw/e.sup.k Equation II
where:
The tendency of the catalyst to produce hydrogen is evaluated by its gas production factor (GPF). This is obtained by measuring the weight of hydrogen produced as a percent of the weight of charge in the above test (Hw).
For conversions of less than 73.3% by volume, the gas production factor is the weight percent of hydrogen as based upon the weight of the charge divided by 0.033.
For conversions equal to or greater than 73.3% and less than 78.0%, volume percent conversion, the gas production factor is given by the following equation (III): EQU GPF=Hw/k Equation III
where:
The greater the carbon production factor, the greater is the tendency of the catalyst to produce carbon and the greater the gas production factor, the greater is the percent of the charge which will be converted into hydrogen, that is the greater is the dehydrogenation property of a catalyst.
A desirable attrition index (AI) and a Carbon Production factor (CPF), and a Gas Production factor (GPF) is an AI (Attrition Index) less than about 24; a GPF of less than about 0.96; and a CPF of less than about 1.1 at a M activity of more than about 60% and preferably at about 65% or higher.
An alternative microactivity test method employs the under 80 mesh microspheres produced as described below, and calcined for three (3) hours at 1050.degree. F. They are contained as a loose body in a reaction chamber, preheated to 900.degree. F. and purged with helium. The liquid feed (D-32 ASTM Standard micro-activity feed) is passed through a preheating section, held at 900.degree. F., and the vaporized oil passed downward through the body of the catalyst at a weight hourly weight ratio of 16. The resultant vapors are condensed in an ice bath. The uncondensed vapors and gases are separated. The body of the catalyst is purged with helium through the above condensation and separation system. The liquid condensate and the gas are analyzed by a gas chromatograph and the coke is analyzed by combustion with oxygen to form the CO.sub.2 which is measured.
The conversion (Cv) which would be produced by employing the same catalyst prepared by the steaming procedure in connection with tthe pellet test described above, is related to the volume percent conversion (Cv)' in the microsphere test described above by the following relation. EQU C.sub.v =(0.973).times.(C.sub.v)'+0.32 Equation IV
The weight percent of the carbon (Cw) by the above pellet test, is related to the weight percent of carbon (Cw).sup.1 by the microsphere test by the following relation: EQU Cw=(0.903).times.(C.sub.w)-0.0444 Equation V
The weight percent of Hydrogen (HW) according to the above pellet test, is related to the weight percent of hydrogen yield (H)' obtained by the above microsphere by the following relation: EQU Hw=(1.02).times.(Hw)'+0.0009 Equation VI
The resultant values of C.sub.v, Cw, and Hw are used to evaluate the CPF and GPF according to Equations I, II, or III.